The present invention relates to an apparatus for controlling a driving force of an electric vehicle.
Conventionally, a vehicle is used on which a brushless DC motor such as a permanent magnet three-phase AC motor using permanent magnets for generating a magnetic field is mounted. In the case where such a vehicle is stopped halfway up a hill while applying a motor torque of a degree at which the vehicle does not reverse, or in a stall state where the traction motor is energized to generate a motor torque but rotation of the traction motor is stopped, a current flows through only a specific phase winding. In this case, among plural switching elements configured by semiconductor devices or the like constituting an inverter for outputting an AC power to drive the traction motor, only a switching element corresponding to the specific phase of the traction motor is set to “ON” state, and the current is supplied to the traction motor via the switching element. Consequently, there arises a problem in that the heat generation which is caused by energization of the windings of the traction motor and the inverter is concentrated into the specific phase winding and the specific switching element.
In order to solve the problem, a drive controlling apparatus for an electric automobile has been proposed in which, when a stall state continues beyond an allowable time period, a process of reducing a torque is conducted to protect a traction motor and power devices such as an inverter, and, when a control of reducing a torque command is to be performed, the reverse speed of the automobile is limited (for example, see Patent literature 1).
Also a motor controlling apparatus for an electric vehicle has been proposed in which, when a stall state is detected, a time period necessary for the junction temperature of a transistor constituting a switching element to reach a given upper limit temperature is calculated, and, when the duration time period of the stall state reaches the calculated time period, a current command value to a traction motor is limited (for example, see Patent literature 2).
Also a motor controlling apparatus for an electric automobile has been proposed in which, when a stall state is detected under the condition that the degree of an accelerator operation by the driver is larger than a predetermined level, the energization amount of a traction motor and a power circuit such as an inverter is limited (for example, see Patent literature 3).
[Patent Literature 1]
                Japanese patent No. 3,106,853[Patent Literature 2]        JP-A-9-56182[Patent literature 3]        JP-A-8-191503        
In the above-mentioned controlling apparatuses of the conventional art, only a process such as that, when a stall state continues beyond a given time period, a torque command value or a current command value is reduced, or that, when a stall state is detected under the condition that the degree of an accelerator operation is larger than a predetermined level, the energization amount is limited is conducted. Consequently, there arises a problem in that the hill climbing ability of a vehicle is impaired. In order to enhance the hill climbing ability of a vehicle, for example, it is required to increase the capacity or heat resistance limit of switching elements constituting an inverter, and enhance the performance of a cooling device for cooling the traction motor and power devices such as the inverter. This causes problems in that the size of the apparatus is increased, and that the cost for configuration of the apparatus is raised.